Ferroelectric Behavior of a Hexamethylenetetramine‐Based Molecular Perovskite Structure

Morita, Hagino; Tsunashima, Ryo; Nishihara, Sadafumi; Inoue, Katsuya; Omura, Yuriko; Suzuki, Yasutaka; Kawamata, Jun; Hoshino, Norihisa; Akutagawa, Tomoyuki

doi:10.1002/anie.201905087

Cited by 71 publications

(58 citation statements)

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“…Although not discussed in the respective papers, DOS calculations shown in refs. [4] and [9] for substituted DABCO materials can be interpreted as a support of this assignment of the lowest CB to the DABCO. The relatively flat bands seen in the calculated band diagram ( Figure 2C) reflect in real-space localization of orbitals and, in particular, localization of the VB.…”

supporting

confidence: 66%

“…[8] These materials are nontoxic, mechanically flexible, and lightweight compared to traditional metal-based halide perovskites. The functionality of these materials has recently been explored as metal-free ferroelectrics, [4,9] mechanical/elastic properties, [10][11][12] and their non-linear optical properties have been reported in a theoretical study. [13] Unfortunately, 17 years after the initial discovery of metal-free halide perovskites, there have been no reports about their charge transport characteristics and only one report (see Supporting Information of ref.…”

mentioning

confidence: 99%

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Metal‐Free Halide Perovskite Single Crystals with Very Long Charge Lifetimes for Efficient X‐ray Imaging

et al. 2020

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X-ray detectors are extensively utilized, including in medical diagnosis, scientific research, and security screening. So far, X-ray detectors have been developed mainly on the basis of metal-based semiconductors. Recently, in addition to traditional Si, Cd(Zn)Te and Ge, crystals based on metal halide perovskites have emerged as a new generation of semiconductors for radiation detection due to their high-Z elements Pb, Bi, and Br. [1-3] However, the requirements for practical wearable materials to be lightweight, economically inexpensive, and environmentally friendly motivate the exploration for nontoxic, low-cost, and simple organic compounds. [4] Lightweight semiconductors based on conjugated molecules or polymers have been demonstrated in a proof-of-principle manner for direct X-ray detection, including 4-hydroxycyanobenzene (4HCB), 1,8-naphthaleneimide (NTI), 1,5-dinitronaphthalene, and rubrene. [5-7] However, the fabrication of large-scale crystals with exceptionally Metal-free halide perovskites, as a specific category of the perovskite family, have recently emerged as novel semiconductors for organic ferroelectrics and promise the wide chemical diversity of the ABX 3 perovskite structure with mechanical flexibility, light weight, and eco-friendly processing. However, after the initial discovery 17 years ago, there has been no experimental information about their charge transport properties and only one brief mention of their optoelectronic properties. Here, growth of large single crystals of metalfree halide perovskite DABCO-NH 4 Br 3 (DABCO = N-N′-diazabicyclo[2.2.2] octonium) is reported together with characterization of their instrinsic optical and electronic properties and demonstration, of metal-free halide perovskite optoelectronics. The results reveal that the crystals have an unusually large semigap of ≈16 eV and a specific band nature with the valence band maximum and the conduction band minimum mainly dominated by the halide and DABCO 2+ , respectively. The unusually large semigap rationalizes extremely long lifetimes approaching the millisecond regime, leading to very high charge diffusion lengths (tens of µm). The crystals also exhibit high X-ray attenuation as well as being lightweight. All these properties translate to high-performance X-ray imaging with sensitivity up to 173 µC Gy air −1 cm −2. This makes metal-free perovskites novel candidates for the next generation of optoelectronics.

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confidence: 66%

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confidence: 99%

Metal‐Free Halide Perovskite Single Crystals with Very Long Charge Lifetimes for Efficient X‐ray Imaging

et al. 2020

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“…+ was believed to be generated in situ by acid (HBr) hydrolysis of hmta: hmtaH + + 3H + + 6H 2 O → 4NH 4 + 6HCHO. [24] ANH 4 [BF 4 ] 3 perovskites were prepared using NH 4 BF 4 with H 3 PO 4 . [15,25]…”

Section: Crystal Synthesismentioning

confidence: 99%

“…It was followed the next year with a paper by Morita et al, who showed ferroelectric behavior in (hmta)NH 4 Br 3 . [24] hmta is also a component of solid fuel tablets and is also known as the active ingredient in pharmaceuticals (urethral disinfectants). hmtaNH 4 Br 3 exhibited ferroelectric behavior up to 400 K. The P-E loops measured using both single crystals ( Figure 3A) and polycrystalline pellets Figure 3B) showed ferroelectric behavior believed to originate from inversion of spontaneous polarization.…”

Section: Ferroelectric Propertiesmentioning

confidence: 99%

“…[25] The single crystals of this compound underwent a phase transition at 333 K (on heating, 323 K on cooling) which was attributed to the motion of the spherical cation (H 2 DABCO) from the completely ordered state at room temperature to the spherical disordered state at higher temperature (Figure 4) A,B) Reproduced with permission. [24] Copyright 2019, Wiley-VCH. A-E) Reproduced with permission.…”

Section: Dielectric Propertiesmentioning

confidence: 99%

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Metal‐Free Organic Halide Perovskite: A New Class for Next Optoelectronic Generation Devices

Song

Hodes

Zhao

et al. 2021

Advanced Energy Materials

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Pb and Sn; X = halogen) was shown to be feasible as sensitizers for photovoltaic cells, [2] and 2012, when conversion efficiencies around 10% were first demonstrated for solid-state cells, [3,4] that the field exploded. Since then, the power conversion efficiency (PCE) of perovskite solar cells has increased to 25.5%, surpassing Cu(In,Ga)Se 2 (CIGS) and cadmium telluride (CdTe), and approaching that of single crystal silicon solar cells. [5] The structural formula of halide perovskite materials is generally ABX 3 , where A and B are two different cations and X is a halide anion (Cl − , Br − , or I −). [6] Currently metal-based organic (usually) halide perovskites have taken a dominant position for optoelectronics due to confluence of several factors, including extremely high optical absorption, long charge lifetimes/diffusion lengths, dominant point defects that only generate shallow levels, and grain boundaries that are essentially benign. [4,7,8] However, these metal-based perovskites do have some intrinsic problems. 1) The toxic solvents involved in fabrication including N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO-not particularly toxic by itself but can transport potentially toxic dissolved species rapidly through the skin), gamma-butyrolactone (GBL), and chlorobenzene. 2) Metal-based perovskites may become available to humans through leaching and transport through water, air, and soil. Toxins like Pb accumulate in the human body and can cause several brain-related symptoms such as memory problems and intellectual disability. [9,10] These toxic materials are not compatible with wearable devices. 3) In general, Pb-based perovskites are prone to attack by moisture, which causes material (and device) degradation. [11,12] Bi-based perovskites are more stable but have relatively poor chargetransport properties. [13] Only recently, metal-free halide organic perovskites, a novel member of the perovskite family, have emerged. [14] Metal-free perovskites take advantage not only of the ABX 3 perovskite structure, but also of the tunability, diversity, and lightweight nature of organic materials. Meanwhile, these materials can be fabricated from aqueous solution and are fully degradable, which hold promise for eco-friendly fabrication and application. Despite the initial discovery of metalfree perovskites in 2002 by Bremner et al., [14] and a similar paper on perchlorate perovskites in 2011, [15] advancements have been reported only during the past 2 years, including Even though the metal-halide perovskites are attracting ever-increasing interest for their breakthrough efficiencies in photovoltaics, light-emitting diodes (LED), X-ray imaging, and general optoelectronics, it was not until very recently that metal-free halide perovskites become recognized, not only for their good optoelectronic performance, but also for their wide chemical diversity, tunability, lightweight, mechanical flexibility, and ecofriendly processability. The community is turning their attention to these lightweight semiconductors, and p...

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PF₆⁻ Pseudohalides Anion Based Metal‐Free Perovskite Single Crystal for Stable X‐Ray Detector to Attain Record Sensitivity

Peng

et al. 2023

Advanced Materials

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Metal-free perovskites (MFPs) possess excellent photophysical properties of perovskites while avoiding the introduction of toxic metal ions and organic solvents, and have been expanded to X-ray detection. However, iodine-based high-performance MFPs are tended to oxidation, corrosion, and uncontrolled ion migration, resulting in poor material stability and device performance. Herein, the strongly electronegative PF 6 − pseudohalide is used to fabricate the large-size MDABCO-NH 4 (PF 6 ) 3 (MDBACO = methyl-N′diazabicyclo[2.2.2]octonium) single crystals (SCs) for solving the problems of iodine ions. After the introduction of PF 6 − pseudohalides, the Coulomb interaction and hydrogen bonding strength are enhanced to alleviate the ion-migration and stability problems. Moreover, combined with theoretical calculations, PF 6 − pseudohalides increase the ion-migration barrier, and affect the contribution of its components to the energy band for a broadening bandgap. Meanwhile, the improved physical properties, such as large activation energy of ionic migration, high resistivity, and low current drift, further expand its application in low-dose and sensitive X-ray detection. Finally, the X-ray detector based on MDABCO-NH 4 (PF 6 ) 3 SCs achieves a sensitivity of 2078 μC Gy air −1 cm −2 (highest among metal-free SCs-based detectors) and the lowest detectable dose rate (16.3 nGy air s −1 ). This work has expanded the selection of MFPs for X-ray detectors and somewhat advanced the development of high-performance devices.

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Ferroelectric Behavior of a Hexamethylenetetramine‐Based Molecular Perovskite Structure

Cited by 71 publications

References 20 publications

Metal‐Free Halide Perovskite Single Crystals with Very Long Charge Lifetimes for Efficient X‐ray Imaging

Metal‐Free Halide Perovskite Single Crystals with Very Long Charge Lifetimes for Efficient X‐ray Imaging

Metal‐Free Organic Halide Perovskite: A New Class for Next Optoelectronic Generation Devices

PF₆⁻ Pseudohalides Anion Based Metal‐Free Perovskite Single Crystal for Stable X‐Ray Detector to Attain Record Sensitivity

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Ferroelectric Behavior of a Hexamethylenetetramine‐Based Molecular Perovskite Structure

Cited by 71 publications

References 20 publications

Metal‐Free Halide Perovskite Single Crystals with Very Long Charge Lifetimes for Efficient X‐ray Imaging

Metal‐Free Halide Perovskite Single Crystals with Very Long Charge Lifetimes for Efficient X‐ray Imaging

Metal‐Free Organic Halide Perovskite: A New Class for Next Optoelectronic Generation Devices

PF6− Pseudohalides Anion Based Metal‐Free Perovskite Single Crystal for Stable X‐Ray Detector to Attain Record Sensitivity

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PF₆⁻ Pseudohalides Anion Based Metal‐Free Perovskite Single Crystal for Stable X‐Ray Detector to Attain Record Sensitivity